In an interview with KSNV in Las Vegas, Pruitt conceded that climate change is a reality and humans have contributed to it "to a certain degree." However, the EPA administrator cast doubt on its negative long-term implications.

"Is it an existential threat? Is it something that is unsustainable, or what kind of effect or harm is this going to have? I mean, we know that humans have most flourished during times of what? Warming trends," Pruitt said. "I think there's assumptions made that because the climate is warming, that that necessarily is a bad thing. Do we really know what the ideal surface temperature should be in the year 2100? In the year 2018? I mean it's fairly arrogant for us to think that we know exactly what it should be in 2100."

The current scientific consensus, according to NASA, is that humans are the primary drivers of climate-warming trends, and that it is "proceeding at a rate unprecedented over decades to millennia." Some of the long-term effects of climate change include a continuing increase in global temperatures, more droughts and heatwaves, stronger and more intense hurricanes, and rising sea levels.

According to the US Global Change Research Program's National Climate Assessment, "climate change presents a global public health problem, with serious health impacts predicted to manifest in varying ways in different parts of the world."

"Public health in the US can be affected by disruptions of physical, biological, and ecological systems," the report explains. "Health effects of these disruptions include increased respiratory and cardiovascular disease, injuries and premature deaths related to extreme weather events, changes in the prevalence and geographical distribution of food- and waterborne illnesses and other infectious diseases, and threats to mental health."

The US has seen a stark shift in its approach to climate change under the Trump administration and at the EPA under Pruitt's leadership. Pruitt has shied away from robust action on climate change, and the phrase "climate change" was not included in the agency's four-year plan.